High School Physics : Electric Circuits

Study concepts, example questions & explanations for High School Physics

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Example Questions

Example Question #1 : Electricity And Magnetism

What is the voltage of a circuit with \(\displaystyle 10A\) of current and \(\displaystyle 20\Omega\) of resistance?

Possible Answers:

\(\displaystyle 30V\)

\(\displaystyle 10V\)

\(\displaystyle 0.5V\)

\(\displaystyle 200V\)

\(\displaystyle 2V\)

Correct answer:

\(\displaystyle 200V\)

Explanation:

For this problem, use Ohm's law: \(\displaystyle V=IR\). In this equation \(\displaystyle V\) is the voltage, \(\displaystyle I\) is the current, and \(\displaystyle R\) is the resistance.

Plug in the given values and solve for the voltage.

\(\displaystyle V=10A* 20\Omega\)

\(\displaystyle V=200V\)

Example Question #1 : Circuit Calculations And Concepts

What is the current of a circuit with a voltage of \(\displaystyle 12V\) and a total resistance of \(\displaystyle 5\Omega\)?

Possible Answers:

\(\displaystyle 2.4A\)

\(\displaystyle 60A\)

\(\displaystyle 4.8A\)

\(\displaystyle 0.42A\)

\(\displaystyle 7A\)

Correct answer:

\(\displaystyle 2.4A\)

Explanation:

For this problem, use Ohm's law: \(\displaystyle V=IR\) . In this equation \(\displaystyle V\) is the voltage, \(\displaystyle I\) is the current, and \(\displaystyle R\) is the resistance.

We can re-arrange the equation to solve specifically for \(\displaystyle I\).

\(\displaystyle \frac{V}{R}=I\)

Plug in the given values for voltage and resistance to solve for the current.

\(\displaystyle \frac{V}{R}=I\)

\(\displaystyle \frac{12V}{5\Omega}=I\)

\(\displaystyle 2.4A=I\)

Example Question #3 : Electricity And Magnetism

What is the resistance in a circuit with a voltage of \(\displaystyle 50V\) and a current of \(\displaystyle 8A\)?

Possible Answers:

\(\displaystyle 400\Omega\)

\(\displaystyle 58\Omega\)

\(\displaystyle 6.25\Omega\)

\(\displaystyle 0.16\Omega\)

\(\displaystyle 42\Omega\)

Correct answer:

\(\displaystyle 6.25\Omega\)

Explanation:

For this problem, use Ohm's law: \(\displaystyle V=IR\) . In this equation \(\displaystyle V\) is the voltage, \(\displaystyle I\) is the current, and \(\displaystyle R\) is the resistance.

We can re-arrange the equation to solve specifically for \(\displaystyle R\).

\(\displaystyle \frac{V}{I}=R\)

Plug in the given values for voltage and current and solve for resistance.

\(\displaystyle \frac{V}{I}=R\)

\(\displaystyle \frac{50V}{8A}=R\)

\(\displaystyle 6.25\Omega=R\)

Example Question #1 : Circuit Calculations And Concepts

\(\displaystyle 9V\) battery is connected to a circuit. The measured current is \(\displaystyle 2A\). What is the equivalent resistance?

Possible Answers:

\(\displaystyle 4.5\Omega\)

\(\displaystyle 0.22\Omega\)

\(\displaystyle 10\Omega\)

\(\displaystyle 18\Omega\)

\(\displaystyle 9\Omega\)

Correct answer:

\(\displaystyle 4.5\Omega\)

Explanation:

For this problem, use Ohm's law: \(\displaystyle V=IR\)

We are given the voltage and current, allowing us to solve for the resistance.

\(\displaystyle 9V=2A* R\)

\(\displaystyle \frac{9V}{2A}=R\)

\(\displaystyle 4.5\Omega=R\)

Example Question #1 : Electricity And Magnetism

A closed electric circuit is set up so that there is a current of \(\displaystyle 9.9A\) and a voltage of \(\displaystyle 30.22V\). What is the resistance in the circuit?

Possible Answers:

\(\displaystyle 0.33\Omega\)

\(\displaystyle 3.05\Omega\)

\(\displaystyle 20.32\Omega\)

\(\displaystyle 299.18\Omega\)

\(\displaystyle 6.1\Omega\)

Correct answer:

\(\displaystyle 3.05\Omega\)

Explanation:

For this problem, use Ohm's law: \(\displaystyle V=IR\).

We are given the current and the voltage. Using these terms, we can solve for the resistance.

\(\displaystyle V=IR\)

\(\displaystyle 30.22V=(9.9A) R\)

\(\displaystyle \frac{30.22V}{9.9A}=R\)

\(\displaystyle 3.05\Omega=R\)

Example Question #4 : Electricity And Magnetism

The current in a circuit is \(\displaystyle 20A\). If the voltage is \(\displaystyle 35V\), what is the total resistance?

Possible Answers:

\(\displaystyle 700\Omega\)

\(\displaystyle 3.5\Omega\)

\(\displaystyle 0.57\Omega\)

\(\displaystyle 1.75\Omega\)

\(\displaystyle 70\Omega\)

Correct answer:

\(\displaystyle 1.75\Omega\)

Explanation:

For this problem use Ohm's law:

\(\displaystyle V=IR\)

We are given the current and the voltage, allowing us to solve for the resistance.

\(\displaystyle 35V=(20A)*R\)

\(\displaystyle R=\frac{35V}{20A}\)

\(\displaystyle R=1.75\Omega\)

Example Question #5 : Electricity And Magnetism

An electrical circuit has a total of \(\displaystyle 3.22\Omega\) resistance and \(\displaystyle 8V\). What is the current?

Possible Answers:

\(\displaystyle 25.76A\)

\(\displaystyle 2.48A\)

\(\displaystyle 11.22A\)

\(\displaystyle 0.089A\)

\(\displaystyle 0.403A\)

Correct answer:

\(\displaystyle 2.48A\)

Explanation:

For this problem use Ohm's law:

\(\displaystyle V=IR\)

We are given the resistance and the voltage, allowing us to solve for the current.

\(\displaystyle 8V=I*(3.22\Omega)\)

\(\displaystyle I=\frac{8V}{3.22\Omega}\)

\(\displaystyle I=2.48A\)

Example Question #6 : Electricity And Magnetism

An electrical circuit has a current of \(\displaystyle 8A\) and \(\displaystyle 32\Omega\) of resistance. What is the voltage?

Possible Answers:

\(\displaystyle 0.25V\)

\(\displaystyle 4V\)

\(\displaystyle 256V\)

\(\displaystyle 128V\)

\(\displaystyle 40V\)

Correct answer:

\(\displaystyle 256V\)

Explanation:

For this problem use Ohm's law:

\(\displaystyle V=IR\)

We are given the resistance and the current, allowing us to solve for the voltage.

\(\displaystyle V=(8A)(32\Omega)\)

\(\displaystyle V=256V\)

Example Question #2 : Electricity And Magnetism

An electrical circuit has a current of \(\displaystyle 13A\) and \(\displaystyle 26\Omega\) of resistance. What is the voltage?

Possible Answers:

\(\displaystyle 338V\)

\(\displaystyle 2V\)

\(\displaystyle 13V\)

\(\displaystyle 0.5V\)

\(\displaystyle 39V\)

Correct answer:

\(\displaystyle 338V\)

Explanation:

For this problem use Ohm's law:

\(\displaystyle V=IR\)

We are given the resistance and the current, allowing us to solve for the voltage.

\(\displaystyle V=(13A)(26\Omega)\)

\(\displaystyle V=338V\)

Example Question #2 : Electric Circuits

A circuit has a current, \(\displaystyle I\), a voltage, \(\displaystyle V\), and a resistance, \(\displaystyle R\). If the voltage remains constant, but the current is doubled (\(\displaystyle 2I\)), what must the new resistance be?

Possible Answers:

\(\displaystyle \frac{1}{2}R\)

\(\displaystyle 2R\)

There is insufficient information to solve

\(\displaystyle 4R\)

\(\displaystyle \frac{1}{4}R\)

Correct answer:

\(\displaystyle \frac{1}{2}R\)

Explanation:

To solve this problem, use Ohm's law:

\(\displaystyle V=IR\)

Since we are doubling the current, but the voltage is remaining the same, we can set our old and new equations equal to each other.

\(\displaystyle I_1R_1=V=I_2R_2\)

We know that the second current is equal to twice the first current.

\(\displaystyle I_2=2I_1\)

Use this equation to substitute current into the first equation.

\(\displaystyle I_1R_1=(2I_1)R_2\)

The initial current now cancels out from both sides.

\(\displaystyle R_1=2R_2\)

Divide both sides by two to isolate the final resistance variable.

\(\displaystyle \frac{1}{2}R_1=R_2\)

 

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